Oil still



April 29, 1930. A. cfvoBAcH ET AL oIL ASTILL Filed Feb. 12, 1927 E@ liv.

INVENTOR ATTORNEYS Arno/d CZ V obac E aye/1e C. Her/ e/ @bgu www.

.Patented Apr. `29, 1930 l p UNITED STATES .PATENT OFFICE ARNOLD 'CHARLES VOBACH, OF WHITING, INDIANA, AND UGENE C. HERTHEL, 0F CHICAGO, ILLINOIS, ASSIGNORS T SINCLAIR REFINING COMPANY, OF CHICAGO,

ILLINOIS, A CORPORATION 0F MAINE oIL STILL This invention relates to improvements in apparatus for the distillation of hydrocar-v bon oils for the production of lighter hydrocarbon oils therefrom. More particularly, the

invention relates to improvements in circulatory oil cracking stills in which a body of oil is maintained at the cracking temperature in a bulk supply tank by circulating the oil from and to the bulk supply tank through a battery of heating tubes connected in multiple, located in a suitable furnace.

In the operation of the improved apparatus of the invention a more even heat absorption by the oil in the various portions of the battery of heating tubes is obtained so that danger of local overheating with consequent formation of carbon deposits on the heated surfaces is minimized and the efficiency and ca acity of the apparatus likewise increased.

epreci'ation of the apparatus and fire hazard due to extreme local overheating and pacity per still over a long period of time may be obtained.

The invention is -of particular application in connection with oil cracking stills of the general character of that described and illustrated in Patent No. 1,285,200 granted to the Sinclair Rening Company, on the application of E. W. Isom, November 19, 1918.

The cracking of heavier hydrocarbon oils by distillation under pressure for the production of lighter hydrocarbon `oils therefrom is accompanied by the formation of fixed gas and carbon, pitch, etc., the character and amount of which are functions of the temperature, the amount increasing rapidly as the temperature necessary to effect the desired cracking -is exceeded. The carbon and pitch formed tends to adhere to the externally heated surfaces of the still insulating them from the cooling effect of the circulating oil. This action is cumulative and may cause extremely high temperatures to be reached in a comparatively short time, which impairs the strength of the material and sometimes causes rupture of the still or tube walls, but in any event necessitates shutting down the still for cleaning.

In the usual practice of cracking oils, as carried out in stills of the type referred to, it

has been found desirable to use oil tempera' tures of about 700 to 800 degrees F. For high eiiiciency and economy it is desirable to extract from the products of combustion the largest possible portion of the heat contained therein. To accomplish this, it is essential that a high average temperature differential be maintained between the heating gases and vthe heat absorbing surfaces with which they contact, thus necessitating` a high initial temperature of the heating gases.

Slnce overheating of any one tube or port1on thereof necessitates the termination of the run, the capacity of the still is limited by thev conditions prevailing at the point subjected to the most severe conditions. Accordingly when the operation is so regulated that the tubes with which the hot gases are first contacted are not subjected to extreme conditions, the remaining tubes which constiute a considerable portion of the total heating surface, are operating considerably below their maximum capacity.

For maximum eiiciency and economy it is therefore desirable, in stills of the character to which the invention relates, to provide for equal distribution of heat absorption through the battery of heating tubes or at 4least to avoid excessive heating in any region and to provide for effective heat absorption throughout. Usually, however, the heating gases are at their maximum temperature as they first contact with the oil containing tubes, their temperature declining as they circulate over succeeding tubes of the battery, so that the temperature difference between the heating gases and the oil containing tubes with which they later contact, is considerably less than duce the desired circulating effect. ln either case, however, the velocity of circulation through the individual tubes is eected to a considerable extent by the temperature to which it isfsubjected. Accordingly, circulae tion through the heating tubes las't exposed to contact with the heating gases tends to become sluggish so that an increased opportunity is afforded for the formation of carbon deposits on the walls of these tubes.

In the apparatus ofthe present invention cores are arranged in and extend through those tubes in the battery intermediate the front and back rows. By this arrangement the cross sectional area of the battery of heating tubes, and particularly of the intermediate rows of tubes, is appreciably reduced and the velocity of circulation and rate of heat transfer correspondingly increased. The ratio of heating surface to volume in the intermediate tubes of the battery is also increased While a proportionally larger volume of oil is circulated through the heating tubes with which the heating gases first contact and which accordingly absorb the greatest amount of heat. A free and unrestricted passage for the circulation of a relatively large volume of oil through the tubes with which the heating gases last contact is nevertheless provided at the same time that the velocity of circulation through these last tubes is increased so that they may be swept clear of carbonaceous material which might otherwise tend to accumulate therein, due to vsluggish circulation, and make or burn onto the walls of the tube as a layer of carbon or coke.

By increasing the average velocity of circulation through all of the tubes in the battery an increased volume of oil is circulated through the tubes with which the heating gases first contact so that both the increased rate 4of heat transfer due to the increased velocity of circulation and the increased volume of oil are effective in increasing the capacity of the still as well as in reducing the temperature of that part of the heat transferring surfaces which is subjected to Vthe `most severe temperature conditions. The increased rate of heat absorption at the heating surfaces subjected to the most extreme conditions also permits-the maintenance of a higher initial temperatu're of the heating gases.

The oil circulating through the intermediate tubes of the battery which 'are vnotconflow. The heat absorbed by the oil in these 'intermediate tubes, which comprise a large velocity of the circulating oi l flowing therethrough, and at the same time greater protection is aorded to the tubes with whichthe.

heating gases irst contact.

The invention will be further described in connection with the accompanying drawings 'ferred to. llt comprises a bulk supply drum 1, adapted to maintain the main body of oil.

being cracked, a vapor line 2 for the escape of vapors of the cracked oil, a battery of heating tubes 3 arranged in a furnace, a circulating ump 4 and circulating connections 5, 6 and? connecting successively the bulk supply drum, the circulating pump, the lower end of the heating tubes, the upper end of the heating tubes and the bulk supply'drum. The vapors escaping from the bulk supply drum to the vapor line 2 may be passed through the reflux tower 8 in which they may be sub] ected to direct contact with fresh oil charged to the still. The vapors from the reflux tower escape through va or line 9 to a condenser 10,

and receiver 11 rom which the distillate and uncondensed vapors and gases may be separately withdrawn. Reflux, and admixed fresh oil when fresh oil is introduced into the Areiiux tower, are returned to the still through connections 12; Fresh oil may be introduced to the upper end of the reflux tower through connection 13. Cool, fresh oil maybe supplied to the bearings of the circulating pump through connection 14 to cool and protectthe same. A connection 15 is provided for pump-` ing out and initially charging the still. A connection v16 is arranged for withdrawing tafr from the still during the operation thereo y The furnace structure comprises a irebox 17 which may be of 'an'yzusual or approved construction furnishing the required amount of heat, an uptake' 18, a downtake heating flue 19 connecting with the stack 20. The battery Aof 011 heating tubes 3 is suspended lvertically in the heating iue 19, the upper header 2l .thereof being supported on I-beams 22 and 23 on top `of the furnace. The heated productsof combustion descending through the heatmg Hue 19 lare caused to circulate back and forth over the heating tubes by means of the baiies 24and 25. -The lower end of thek heating flue is closed by a partition or floor 26 arranged somewhat above the lower end of the heating tubes and supported thereby. The upper end of the heatmg Hue is closed by partition 27 arranged in the opening in the top of the furnace through which the heating tubes depend, this partition as well as the baHles 24 and 25 being supported by the heating tubes. The heating tubes 3 of the battery are thus suspended -from their upper end and may expand or contract freely with changes of temperature. The battery of heating tubes may likewise be removed as a unit through the opening at the top of the furnace for the purpose of inspection and repair.

The distance between the baHle 24 and the top of the heating Hue is greater than the distance between the baHies 24 and 25 and this latter distance in turn is greater than the distance between the baille 25 and the bottom of the heating Hue so that the velocity of the heating gases is progressively increased through the successive passes in the heating Hue as the temperature of the heating gases falls, thereby compensating to a greater or less extent for the decreased heating effect of the heating gases as their temperature declines. The front tubes in the battery of heating tubes are prevented from receiving an undue amount of heat by direct radiation' header.A The upper headers 21 are provided with removable plugs 30 arranged to register with the end of the heating tubes 3 so that the cores may be readily removed and the tubes cleaned. In the operation of the apparatus of th invention o1l is circulated from the bulk supply drum 1 by means of the circulating pump 4 to the lower end of the heating tubes 3 and thence upwardly therethrough and back to the bulk supply drum from the upper end of the heating tubes. Circulation is assisted by the progressive heating of the oil as it Hows upwardly through the heating tubes. The hot products vof combustion arising'from the Hrebox ,are first contacted with the upper end of the heating tubes through which a large volumeof oil is being circulated at increased velocity and which are accordingly capable of the greatest heat absorption without objectionable overheating, the gases then circulating back and forth over the heating tubes downwardly to the connection with the stack. A free'and unobstructed How is nevertheless maintained through the heating tubes with which the coolest heating. gases 4are contacted wardly through the heating Hue and as their temperature decreases due to the absorption of heat by the circulating oil, by the progressively decreasing area of the passage through which they are required to circulate.v

We claim:

1. In tubular oil cracking stills, a heatin Hue, a firebox connected to one end of the heating Hue and a stack Hue connected to the other end thereof, a battery of oil heating tubes connected in multiple arranged in and extending through the heating Hue whereby heatin gases passing from the Hrebox to the stack ue pass thereover in the heating H'ue, means for circulating oil through the oil heating tubes in multiplel and in'a direction generally countercurrent to the How of heating gases thereover, and cores arranged in and extending through the oil heating tubes in the said heating Hue except those tubes immediately adjacent the Hrebox and the stack Hue.

2. In tubular oil cracking stills, a heating Hue, a Hrebox connected to one end of the heating Hue and a. stack Hue connected to the other end thereof, a battery of oil heating tubes connected in multiple arranged in and extending through the heating Hue whereby heatin gases passing from the irebox to the stack ue pass `thereover in the heatino` Hue, means for circulating oil through the oi heating tubes in multiple and in a direction generally countercurrent to the How of heating gases thereover, the intermediate oil heating tubes in the said heating Hue having cores located centrally therein and extending longitudinally therethrough whereby the cross sectional area of the intermediate tubes is decreased and the velocity of circulation therethrough increased.

3. In tubular oil cracking stills, a heating Hue. a firebox connected to one end of the heating Hue and a stack Hue connected to the other end thereof, a battery of oil heating tubes connected in multiple arranged in and extending through the heating Hue whereby heating gases passing from the Hrebox to the stack Hue pass thereover in the heating Hue, the oil heating tubes first exposed to the heating gases from the irebox in the heating Hue having a free, unobstructed passage therethrough and the intermediate heating tubes of the battery having cores centrally located therein and extending therethrough.

4. In an oil cracking still a furnace having a heating Hue connected at one end to arebox and at the other end to a stack Hue, a battery of heating tubes connected in multiple arranged in and extending through the heating flue in the furnace, a still drum and connections including a pump for circulating oil therefrom through the heating tubes of the battery in multiple and back to .the still drum, and cores located and. extending through the heating tubes in the said heating flue except those first exposed to the heating gases from the irebox and those last exposed to the heating gases passing 'from the heating iue to the stack ilue.

5. 1n an oil cracking still a furnace having a heating flue connected at one end to a iirebox and at the other end to a stack flue, a battery of heating tubes connected in multiple arranged in and extending through the heating flue in the furnace, a still drum and connections including a pump for circulating oil therefrom through the heating tubes of the battery in multiple and back to the still drum, baies lin the heating Hue for causing gases from the firebox to HOW over the heating tubes in a series of passes, and cores located and extending lthrough the heating tubes in the said heating flue except those first exposed to the heating gases from the frebox and those last exposed to the heating gases passing from the heat-ing iue to the stack iue.

ARNOLD CHARLES VOBACl- EUGENE C. HERTHEL. 

